Compact optical system and packaging for head mounted display

ABSTRACT

A head mounted virtual image display unit is provided which is compact in size and weight, and incorporates a high performance optical system offering a clear see-through capability. A sliding light shield may be incorporated for those instances when see-through capability is not desired. A focus adjustment may be incorporated to permit the focusing of the image, for example, at a distance of approximately 18 inches to infinity. An adjustable headband may be incorporated that adapts to fit the users head. A flexible boom structure may be incorporated to facilitate fine positional adjustment of the optical assembly. A slider and ball joint mechanism may also be incorporated to facilitate positional adjustment of the optical assembly. A built-in microphone may be incorporated to enable speech input by the user. The head mounted virtual image display unit may be used comfortably in conjunction with eye or safety glasses, and provides a useful image to the user without blocking his view of the surrounding environment. The unit is designed to have a pleasing appearance so as to greatly enhance user acceptability.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.09/626,749, filed Jul. 27, 2000, now U.S. Pat. No. 6,747,611, thedisclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to compact optical systems and,more particularly, to compact optical systems for use in displaydevices, for example, personal devices such as wearable personalcomputer systems, head mounted displays, portable telephones and thelike.

BACKGROUND OF THE INVENTION

Virtual image displays combine magnifying optics with a small imagepanel to provide the viewer with a virtual image capable of displayinglarge amounts of information. Such displays have found application in socalled head mounted displays and are used in conjunction with acomputer-based device for a variety of applications. As is known, thecomputer-based device includes processing and display driver circuitryfor generating the image signal to be displayed via the optics and imagepanel.

However, such conventional virtual image displays are known to have manyshortcomings. For example, such displays have suffered from being tooheavy for comfortable use, as well as too large so as to be obtrusive,distracting, and even disorienting. These defects stem from, among otherthings, the incorporation of relatively large optics systems within themounting structures, as well as physical designs which fail toadequately take into account such important human factors as size,shape, weight, etc.

Examples of some conventional head mounted virtual displays are shown inFIGS. 1 and 2. FIG. 1 illustrates a head mounted virtual display unit 10which rests on the users head and face in a manner similar to that of apair of eye glasses. The user views virtual images through the displayportion 12. Nose bridge 14 and side supports 16 serve to provide supportfor the display while on the users head and face. The unit 10 may beconnected to a computer via connector 18. It is known that such a unitis cumbersome and permits the wearer to see substantially nothing otherthan the display screen. That is, the user is unable to view hisimmediate environment. Such a head mounted virtual display is disclosedin an international patent application identified as WO 95/11473, thedisclosure of which is incorporated herein by reference.

FIG. 2 illustrates a head mounted monocular virtual display unit 20. Thesupport structure 12 is positioned on a users head and the displayportion 14 comes down in the users field of vision. This design is alsoknown to be cumbersome and likely to obstruct the users surroundingview. Such a head mounted monocular virtual display is also disclosed ina the international patent application identified as WO 95/11473.

Other examples of conventional compact display systems and head mounteddisplays are disclosed in U.S. Pat. No. 5,771,124 to Kintz et al., U.S.Pat. No. 5,757,339 to Williams et al., and U.S. Pat. No. 5,844,656 toRonzani et al., the disclosures of which are incorporated herein byreference. Still further, it is known that Sony Corporation makes a headmounted virtual display known as the “Glasstron.”

However, all of the examples given suffer from one or more of theabove-mentioned design deficiencies. As a result, such deficiencies haveseriously hindered the general acceptance of such devices.

Compact optical systems for use in virtual display applications whichimprove upon the previously existing art are described in two U.S.patent applications assigned to the present assignee and identified asU.S. Ser. Nos. 09/437,972 and 09/437,793, both filed on Nov. 10, 1999,the disclosures of which are incorporated herein by reference.

Nonetheless, there is a need for a compact optical system for use indisplay devices, for example, personal devices such as wearable personalcomputers, head mounted displays, portable telephones and the like,which substantially reduces or eliminates the above-mentioneddeficiencies as well as others not specifically mentioned associatedwith the existing art, and/or which improves upon the compact opticalsystem designs described in the above-referenced U.S. patentapplications identified as U.S. Ser. Nos. 09/437,972 and 09/437,793.

SUMMARY OF THE INVENTION

The present invention provides an optical system design for use indisplay devices such as, for example, a head mounted virtual imagedisplay, that remedies defects exhibited by conventional designs, e.g.,prohibitive size and weight, obstructed view, etc. Such a novel design,for example, makes possible wearable computer systems of greaterconvenience and acceptability to a wide range of users.

In accordance with one embodiment of a compact optical system of theinvention for directing an image signal for viewing by a user, whereinthe image signal is generated in accordance with a microdisplay, theoptical system comprises: a beam splitting prism positioned proximate tothe microdisplay; a field lens positioned between the beam splittingprism and the microdisplay; a negative lens positioned between the fieldlens and the beam splitting prism; a reflective lens positionedproximate to the beam splitting prism, on a side of the beam splittingprism opposite the microdisplay; and a quarter wave plate positionedbetween the reflective lens and the beam splitting prism; wherein thebeam splitting prism, the field lens, the negative lens, the reflectivelens and the quarter wave plate are arranged such that the image signal,linearly polarized in accordance with the microdisplay: (a) passesthrough the field lens and the negative lens; (b) enters the beamsplitting prism substantially passing through a polarizing surface ofthe beam splitting prism; (c) passes through the quarter wave platebecoming circularly polarized; (d) reflects at a surface of thereflective lens back toward the quarter wave plate passing through thequarter wave plate a second time becoming linearly polarized with apolarization direction rotated by 90 degrees with respect to an originallinear polarization direction associated with the image signal; and (e)reenters the beam splitting prism substantially reflecting at thepolarizing surface of the beam splitting prism and exits the beamsplitting prism for viewing by the user.

In accordance with one embodiment of a head mounted virtual imagedisplay unit according to the invention, the display unit is compact insize and weight, and incorporates a high performance optical system,such as the optical system described above, offering a clear see-throughcapability. A sliding light shield may be incorporated for thoseinstances when see-through capability is not desired. A focus adjustmentmay be incorporated to permit the focusing of the image, for example, ata distance of approximately 18 inches to infinity. An adjustableheadband may be incorporated that adapts to fit the users head. Aflexible boom structure may be incorporated to facilitate finepositional adjustment of the optical assembly. A slider and ball jointmechanism may also be incorporated to facilitate positional adjustmentof the optical assembly. A built-in microphone may be incorporated toenable speech input by the user.

It is to be appreciated that the head mounted virtual image display unitmay be used comfortably in conjunction with eye or safety glasses, andprovides a useful image to the user without blocking his view of thesurrounding environment. The unit is designed to have a pleasingappearance so as to greatly enhance user acceptability.

It is to be further appreciated that a head mounted virtual imagedisplay unit may be combined with a computer-based device. Thecomputer-based device may generate and provide an electrical signal to amicrodisplay associated with the display unit for use in generating theimage signal to be viewed by the user. The combination advantageouslyforms a portable computer system.

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional eye glass type head mounted virtualdisplay;

FIG. 2 illustrates a conventional monocular type head mounted virtualdisplay;

FIG. 3A illustrates a first view of a head mounted virtual display unitand computer-based device according to one embodiment of the presentinvention;

FIG. 3B illustrates a second view of a head mounted virtual display unitand computer-based device according to one embodiment of the presentinvention;

FIG. 4 illustrates an artistic rendering of a head mounted virtualdisplay unit according to the present invention as may be worn by auser;

FIG. 5 illustrates a virtual display optical system according to anembodiment of the present invention;

FIGS. 6A through 6C illustrate graphs highlighting performance of anoptical system according to an embodiment of the present invention interms of its astigmatism, distortion, and lateral color;

FIG. 7 illustrates a table of design parameters of an optical systemaccording to an embodiment of the present invention;

FIG. 8 illustrates an integrated focus mechanism and placement of amicrophone in a head mounted virtual display according to an embodimentof the present invention;

FIGS. 9A and 9B illustrate a sliding light shield in the open and closedpositions, respectively, on a head mounted virtual display according toan embodiment of the present invention; and

FIG. 10 illustrates headband and pod/boom adjustment mechanisms on ahead mounted virtual display according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An optical system design of the present invention will be explainedbelow in the context of a head mounted virtual image display unit andwearable computer. However, it is to be understood that the presentinvention is not limited to this or any particular display application.Rather, the invention is more generally applicable to any suitabledisplay application in which it is desirable to utilize a compactoptical system for displaying images which may be incorporated into adevice used in the application. Such devices may be, for example,personal devices such as wearable personal computers, head mounteddisplays, portable telephones and the like.

Referring initially to FIGS. 3A and 3B, a head mounted virtual displayunit 10 and computer-based device 20 according to one embodiment of thepresent invention are shown. A cable 30 is provided for electricallycoupling the computer-based device 20 with the head mounted virtualdisplay unit 10. FIGS. 3A and 3B illustrate the same head mountedvirtual display unit 10, but from opposing views. It is to be understoodthat the computer-based device 20 preferably has a small form factor,e.g., pocket-sized, and is lightweight. It may also preferably have aclip for attachment to a user's belt or pocket. Such a computer-baseddevice is referred to as a “wearable computer.” The wearable computermay include all or most of the typical components available in apersonal computer, laptop computer, personal digital assistant or thelike, e.g., a processor (e.g., CPU), fixed memory, removable memory,display driver circuitry, external network (e.g., Internet) connectiondevice, application software, etc.

The head mounted virtual display unit 10 comprises: an optical module100; a flexible boom 200; an adjustment pod 300; an earpiece 400; and ahead band 500. According to a preferred embodiment of the invention, theoptical module 100 comprises an optical system, a focus mechanism, asliding light shield and an integrated microphone. The flexible boom 200enables fine positional control of the optical module 100 in front ofthe user's eye. By way of example, a metal or plastic, spiral-woundgooseneck tubing may be used as the flexible boom. Such tubing is wellknown and commercially available. The adjustment pod 300 preferablycontains a combination sliding and ball joint mechanism for controllingof the boom position and angle. This embodiment will be explained inmore detail below in the context of FIG. 10. Of course, otherarrangements for affecting positional control of the optical module maybe employed. The earpiece 400 is shown attached to the pod 300 by meansof a connecting wire. Alternatively, it may be attached to the pod 300with its output directed towards the user's ear, or attached on a swingdown lever from the pod 300. The headband 500 is shown with adjustmenttabs 502 and head grips 504. The headband is normally worn around theback of the head, however, alternate arrangements are possible. Forexample, the band may go over the top of the head or, alternatively, thepod 300 may be attached to a helmet (not shown).

It is to be appreciated that the flexible boom 200 and adjustment pod300 permit the user to move the optical module 100 into and out of thefield of view of, in this case, his right eye. Of course, the unit 10may be configured such that the optical module 100 is viewed by awearer's left eye. In such case, the unit 10 can be turned over to beused by the left eye. Also, the unit 10 may be configured to include twoseparate display portions, that is, one for the right eye and one forthe left eye. One or ordinary skill in the art will realize otherconfigurations.

Thus, the combination of the display unit 10 and the computer-baseddevice 20 permits a user to view visual data generated in accordancewith the device 20, e.g., from application software, web browser, etc.The visual information is provided to the display via cable 30. Theearpiece 400 permits a user to listen to audio data generated inaccordance with the device 20. The microphone (shown in FIG. 8) in theoptical module 100 permits a user to input voice commands to thecomputer.

Accordingly, FIGS. 3A and 3B illustrate a light weight wearable computersystem comprising a light weight head mounted display unit containing acompact optical system used in conjunction with a pocket sized, wearablecomputer. Since the optical system is attached to the user's head bymeans of a light weight boom or band structure, such as shown, thisenables a total head mounted display weight of approximately two ouncesor less to be achieved.

FIG. 4 illustrates an artistic rendering of a head mounted virtualdisplay unit 10 according to the present invention as may be worn by auser. As shown, the optical module 100 may be advantageously moved intothe field of view of the user's right eye or left eye. It is small so asto be unobtrusive and allows an undistorted view through the opticalsystem to the outside world. When the display is turned on, there isenough light that the display can be seen clearly against thesurroundings.

A preferred optical system according to the present invention for use inthe optical module 100 will now be described. It is to be understood,however, that the inventive optical system design may be used inaccordance with devices other than the wearable computer systemillustrated in FIGS. 3A and 3B. Given their compact form factors andability to display high quality optical images, the optical system ofthe invention is suitable for a vast number of applications. One ofordinary skill in the art will realize various other implementations andapplications with which such an inventive optical system may beemployed.

Further, as will be explained in detail in connection with the followingembodiment, the optical system of the invention provides optics withfolded light paths which are “on-axis” optics rather than “free form”optics. In this manner, the optical system is able to provide theadvantages and features described herein, as well as others that one orordinary skill in the art will realize given the inventive teachingsherein. It is to be appreciated that by the terms “on-axis” and “freeform,” we mean the following. A ray going through a typical sphericallens that is normal to the lens and passes through its center, definesthe optical axis. The bundle of rays passes through the lens clusterabout this axis and may be well imaged by the lens. Examples of systemsmight be a camera, microscope, or binoculars. In more complex systems,the bundle of rays may cluster about a line tilted with respect to thelens; this would be “off-axis” imaging. Note, the typical spherical lensis symmetric about the optic axis. Yet other systems are not radiallysymmetric and do not have a clear optical axis as defined above, yet maystill perform an imaging function. We generally call them “free form”optics.

Referring now to FIG. 5, a virtual display optical system according toan embodiment of the present invention is shown. As previouslymentioned, this optical system is preferably the optical system that isemployed in the optical module 100. Light from a light source 1000,typically a cluster of red, green and blue light emitting diodes (LEDs),illuminates a microdisplay 1100. In this embodiment, the microdisplay isa transmissive type microdisplay. Transmissive microdisplays that may beused in accordance with the invention are available, for example, fromKopin of Taunton, Mass. It is to be appreciated that the transmissivemicrodisplay may be replaced with an emissive microdisplay wherein thelight source is internal to the microdisplay. Emissive microdisplaysthat may be used in accordance with the invention are available, forexample, from Planar of Beaverton, Oreg. Also, the microdisplay may be areflective type microdisplay. Reflective microdisplays that may be usedin accordance with the invention are available, for example, fromColorado Microdisplay of Boulder, Colo.

In any case, as is well known, the microdisplay creates an image inresponse to electrical signals applied to the display. The electricalsignals may, for example, be provided to the microdisplay from thecomputer-based device 20 (FIGS. 3A and 3B). This image is viewed bymeans of a field lens 1200, a negative lens 1300, a beam splitting prism1400, a quarter wave plate 1600 and a reflective lens 1500. As is wellknown, a negative lens includes one or more outer surfaces having aconcave form, as compared to a positive lens which includes one or moreouter surfaces having a convex form. Light from the display is linearlypolarized and travels through lenses 1200 and 1300 entering the prism1400. The polarization of the light is such that the light issubstantially transmitted through a polarizing surface 1410 of prism1400. The light then passes through the quarter wave plate 1600 andbecomes circularly polarized. The reflective lens 1500 has a reflectivecoating (e.g., metallic or dielectric reflective material) at its curvedsurface that reflects light back towards the quarter wave plate 1600.Upon passing through the quarter wave plate 1600 a second time, thelight once again becomes linearly polarized, however, its polarizationdirection has now been rotated by 90 degrees. The light reenters theprism 1400 and is now substantially reflected by polarizing surface1410. The light leaves the prism 1400 and approaches the exit pupil 1700of the optical system. The optical system exit pupil 1700 is where theuser normally positions their eye to view the virtual image of themicrodisplay 1100.

It is a feature of this design that the eye, in looking through theoptical system to the outside world, does not see a distorted view. Thisis achieved by a design feature of the invention whereby the shapes ofthe entry surface 1420 and exit surface 1430 of prism 1400 are designedto be of substantially the same shape or form for this purpose.

It is also a feature of this optical system that the light from themicrodisplay 1100 forms a virtual image at the exit pupil 1700, and thatthe image is of high quality and substantially free of aberration. Thatis, the virtual image is essentially free of astigmatism, essentiallyfree of lateral distortion, and essentially free of lateral coloraberration.

This high performance is achieved by combining the field lens 1200, thenegative lens 1300, the prism 1400, the quarter wave plate 1600 and thereflective lens 1500 in the arrangement shown and by proper selection ofmaterials for these elements. In particular, the negative lens 1300material is chosen to work in combination with the field lens 1200 andreflective lens 1500 to essentially eliminate lateral color aberration.The preferred design parameters associated with these lens, as well asthe other elements of the optical module, will be given below in thecontext of FIG. 7.

FIGS. 6A through 6C show three respective graphs of the optical systemperformance of the optics shown in FIG. 5. In FIG. 6A, a graph ofastigmatism versus field position is shown. It is apparent that imagefield is flat within 0.016 millimeters (mm), and that there is less than0.005 mm of astigmatism between the sagital and tan gential directions.This means the image is essentially perfectly flat and essentiallywithout astigmatism. FIG. 6B shows a graph of distortion versus fieldposition. From this graph, we see that the optical system has less than0.2 percent distortion across the field. For those skilled in the art,this means the image is essentially distortion free. FIG. 6C shows agraph of the lateral color versus field position. We see that at themaximum field position there is less than 0.003 mm difference inposition between red, green, and blue colors. The microdisplay of apreferred embodiment has a pixel pitch of approximately 0.012 mm.Therefore, the optical system is essentially free of lateral coloraberration.

FIG. 7 illustrates a table of design parameters of an optical systemaccording to a preferred embodiment of the present invention. The tablegives the surface number (column A), the surface radius or curvature(column B), the center thickness of surface (column C), the apertureradius of surface (column D) and the material (column E) for eachoptical element in the system. In the table, SRF refers to “surface;”OBJ refers to “object position;” AST refers to “aperture stop;” IMSrefers to “image surface;” and BK7 and SF1 are industry standard glasstypes. It also gives the spacing between the elements. It is to beappreciated that the surfaces listed in the table (by surface number incolumn A) are surfaces of the components (e.g., beam splitting prism,field lens, etc.) of the optical system shown in FIG. 5. Thecorrespondence between the components of FIG. 5 and the surfaces isdenoted down the left hand side of FIG. 7 by the bracket andcorresponding reference numeral of the component from FIG. 5. With thisdesign data, one skilled in the art would be able to implement andverify the aforementioned performance of the optical system.

Referring now to FIG. 8, an integrated focus mechanism and placement ofan integrated microphone in a head mounted virtual display according toan embodiment of the present invention is shown. As previouslymentioned, these components are housed in the optical module 100 shownin FIGS. 3A and 3B. It is to be understood that FIG. 8 illustrates thefocus mechanism and microphone with the outer casing (housing) of theoptical module 100 removed. With respect to the integrated focusfeature, a compact carriage mechanism translates the field lens 1200,microdisplay 1100 and LED backlight 1000, shown in FIG. 5, such as tofocus the virtual image at a distance of approximately 18 inches toinfinity. The field lens 1200, the microdisplay 1100 and the backlight1000 are mounted in the movable carriage 2200. The carriage 2200 istranslated along the optical axis by means of a screw 2500 and knob2600. Other conventional translation actuators arrangements may beemployed. A motion of ±1 mm of the carriage 2200 relative to the beamsplitting prism 1400 is sufficient to adjust the image focus over thedesired range. It is to be appreciated that the negative lens 1300, thebeam splitting prism 1400, the quarter wave plate 1600 and thereflective lens 1500 (located under the endcap of module housing andthus not visible in FIG. 8) remain fixed inside the housing of theoptical module.

Also, FIG. 8 illustrates the placement of a compact microphone 2700. Themicrophone may be of the directional type. It is pointed towards theusers face and away from the surrounding environment such as to pick upthe voice of the user. It is to be appreciated that wiring for themicrophone and for the optical system may be run through the flexibleboom 200. As previously mentioned, the components in the optical module,as well as the earpiece 400 may be coupled to a computer-based device 20via a cable 30 (FIGS. 3A and 3B).

FIGS. 9A and 9B illustrate a sliding light shield in the open and closedpositions, respectively, on a head mounted virtual image displayaccording to an embodiment of the present invention. In particular,FIGS. 9A and 9B show a detailed view of the optical module 100 with alight shield integrated with the housing of the optical module. In FIG.9A, a light shield 3200 is shown in the open position (see-throughmode). Thus, a user viewing an image through the optics of the opticalmodule 100 is able to see light emanating from behind the optical module100. As shown, the beam splitting prism 1400 is visible in FIG. 9A withthe light shield 3200 in the open position. In FIG. 9B, the light shield3200 is shown in the closed position, thus blocking or substantiallyblocking the background light. The light shield 3200 may be slid by theuser along the direction indicated by arrow A when it is desired toreduce or eliminate the background light. It is to be appreciated thatthe external light modifying shield may be opaque, partially opaque,colored or polarizing as desired by the application being executed inaccordance with the virtual display system.

FIG. 10 illustrates headband and pod/boom adjustment mechanisms on ahead mounted virtual display according to an embodiment of the presentinvention. Specifically, FIG. 10 shows a detail of the podiboomadjustment mechanism. As shown, the adjustment pod 300 comprises a baseportion 4100 having a channel 4110 formed therein. Inside the channel4110 is fitted a slider mechanism 4200 which is capable of sliding backand forth the length of the channel, as denoted by the direction arrow4400. Small circular indentations 302 (visible in FIG. 3B) mate with oneor more corresponding protrusions on the inner side of the slidermechanism (not shown) to allow the slider mechanism, and thus theoptical module 100, to remain in a desired position.

Further the pod assembly comprises a ball joint 4300 pivotably fitted inthe slider mechanism 4200. The pivotable ball joint 4300 allows the podassembly, and thus the optical module 100, to rotate, as denoted by thedirection arrows 4500 and 4600. The flexible boom 200 also allows theoptical module to be moved in any of the directions denoted by arrows4400, 4500 and 4600. By incorporating the slider and ball jointmechanism and flexible boom, the user may adjust the optical module 100to any particular distance and/or position he so desires, with respectto his eye, in an optimal manner.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may beaffected therein by one skilled in the art without departing from thescope or spirit of the invention.

1. A compact head mounted virtual image display unit, the unitcomprising: a microdisplay; an optical system for directing an imagesignal for viewing by a user, the image signal being generated inaccordance with the microdisplay; an optical system mounting structurefor supporting the optical system within the field of view of only asingle eye of the user; a housing to substantially contain at least theoptical system; and a slidable opaque light shield, integrated withinthe housing and having an open position and a closed position, whereinthe opaque light shield is slidable along a length of an exterior wallof the housing and slidably positioned with respect to the opticalsystem such that, in the open position, the image signal is viewed bythe user together with background light entering the optical system, andin the closed position, the image signal is viewed by the user withbackground light blocked from entering the optical system and therebyeliminated.